<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>IFE task 22</title>
    <style>
        body {
            text-align: center;
        }

        .tree {
            width: 80%;
            height: 300px;
            margin: 20px auto;
        }

        div {
            margin: 36px 20px;
            border: #fb6b0b solid 2px;
            display: -webkit-flex;
            display: flex;
            -webkit-flex-grow: 1;
            flex-grow: 1;
            transition: background-color 1000ms;
        }
    </style>
</head>
<body>
    <div class="tree">
        <div>
            <div>
                <div></div>
                <div></div>
            </div>
            <div>
                <div></div>
                <div></div>
            </div>
        </div>
        <div>
            <div>
                <div></div>
                <div></div>
            </div>
            <div>
                <div></div>
                <div></div>
            </div>
        </div>
    </div>
    <form>
        <select>
            <option value="DLR">前序</option>
            <option value="LDR">中序</option>
            <option value="LRD">后序</option>
        </select>
        <button type="button">开始遍历</button>
    </form>
    <script src="js/Task22.js"></script>
</body>
</html>